Pacing instruments can be used to treat patients suffering from various heart conditions that may result in a reduced ability of the heart to deliver sufficient amounts of blood to a patient's body. These heart conditions may lead to rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these conditions, various devices (e.g., pacemakers, defibrillators, etc.) can be implanted in a patient's body. Such devices may monitor and provide electrical stimulation to the heart to help the heart operate in a more normal, efficient and/or safe manner.
Pacing the heart at a fixed rate is limiting because it does not allow the heart rate to increase with increased metabolic demand. If the heart is paced at a constant rate, as for example by a VVI pacemaker, limitations are imposed upon the patient with respect to lifestyle and activities. It is to overcome these limitations and improve the quality of life of such patients that rate-responsive pacemakers have been developed.
Rate responsive capable pacemakers often include one or more sensors to gain insight into the current metabolic demand of the patient, and adjust the pacing rate accordingly. This can be accomplished relatively easily in a traditional pacemaker that has a pacemaker “can” implanted in a pocket under the skin, with leads extending into the heart. The pacemaker “can” is often sufficiently large to house a fairly high capacity battery and may have significant processing power. Also, the pacemaker may have access to signals and/or sensors that are located both inside the heart via the leads and outside of the heart via the “can”.
Leadless Cardiac Pacemakers (LCP), which are implanted in or proximate to the heart, present a unique challenge to rate responsive pacing. For example, because of constant movement of the LCP with the heart, accelerometer data obtained from a local accelerometer within the LCP housing may have significant noise, which can require significant processing power to isolate movement that is due to the patient's activity versus movement cause by the beating of the heart itself. In another example, because of its location and size, it can be difficult for an LCP to derive a reliable measure of respiration rate and/or tidal volume of the patient, which can be an indicator of patient activity. These are just some of the challenges in providing effective rate responsive pacing in a LCP. What would be desirable are improved systems and methods for providing rate responsive pacing using a Leadless Cardiac Pacemaker (LCP).